Formation mechanism of tetragonal nanoprecipitates in Fe–Ga alloys that dominate the material's large magnetostriction

Up to now, the formation mechanism of tetragonal nanoprecipitates that may dominate the large magnetostriction of Fe–Ga alloys remains unclear. Here we found that both L6₀- and D0₂₂-type face-centered-tetragonal nanoprecipitates are precursors of the face-centered-cubic L1₂ equilibrium phase, as identified in the isothermally-aged Fe₇₃Ga₂₇ and Fe₇₄Ga₂₆ alloys, respectively. The L6₀ phase is formed due to Ga ordering along <001>-A2 direction and simultaneous lattice distortion. The D0₂₂ phase is formed via diffusionless lattice distortion when the D0₃ ordering degree is sufficient high. These findings may provide a microstructural basis for the large magnetostriction induced by soluting nonmagnetic Ga into body-centered-cubic Fe.